Thermal and hydrothermal stability of a metal monolithic anodic alumina support for steam reforming of methane

Abstract

In this work, a plate-type Al/Fe–Cr alloy/Al clad material was prepared into a metal-monolithic anodic alumina support (Al 2O 3/Fe–Cr alloy/Al 2O 3) to investigate its thermal and hydrothermal stability and potential use in the steam reforming of methane (SRM). re-heating of the base material at 500 °C for 3 h or longer significantly enhanced the thermal resistance temperature of the support, which was associated with the formation of the diffusion layer between the alumina layer and the alloy layer. Pore widening treatment (PWT) in 4.0 wt.% oxalic acid solution at 20 °C for 4–8 h provided an excellent anodic support that was strong enough to endure a 1000 °C calcination without the alumina layer shelling off. The appearance of an increased number of smaller fragments and cracks on the support surface was considered to be one of the main reasons for the promotion effect of PWT. During a thermal shock test of the heating–cooling cycles from ambient temperature to 800 °C for 5000 times, no alumina layer was found to shell off from the alloy interlayer, which highlighted the good adhesion between the alumina layer and the alloy layer in the anodic alumina support. Although an obvious decrease of surface area was observed when calcining the support in air or steam at 700 °C, the anodic alumina-supported Ni catalyst showed favorable catalytic durability and hydrothermal stability in the stationary SRM test for 3000 h and the DSS-like (daily start-up and shut-down) test for 500 times in a typical hydrothermal environment (700 °C, Steam/Carbon = 3, 157,000 mL/(h g)). Especially, under an electrical-heating pattern, the SRM reaction system could reach stability within ca. 10 min, offering a strong possibility for shortening the start-up time of conventional SRM reformers from 1 to 2 h to a few minutes.